There are different types of logic gate, depending upon what the gate is needed to do.
OR gates
An OR gate will give a high output if any of the inputs is high. For example, in a simple lighting circuit with two switches in parallel the lamp will light if either switch is pressed.
The relationship between the inputs and the output can be captured in a truth table. A and B represent the inputs and Q is the output.
OR gate symbol
AND gates
An AND gate will give a high output only if all of the inputs are high. For example, in a simple lighting circuit with two switches in series the lamp will light only if both switches are pressed.
Not gates
A NOT gate is slightly different because it has just one input. It will give a high output if the input is low. This could be represented by a simple lighting circuit with a push-to-break switch: if the switch is pressed then the lamp will turn off. NOT gates are often used in emergency-stop buttons on machine tools.
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